Laser printers and other electrophotographic image forming devices use toner particles to form a desired image on print media. The print media is often paper, although a wide variety of different print media may be employed. Once the toner is applied to the media, the media is advanced along a media path to a thermal fuser. In some image forming devices, the fuser includes a fuser roller and a mating pressure roller. As the media passes between the fuser roller and the pressure roller, the toner is fused to the media through a process using pressure and heat exceeding 300.degree. F. (148.degree. C.).
The interference area between the fuser roller and the pressure roller is often referred to as the nip. It is desirable to maintain a substantially uniform pressure in the nip. Uneven or non-uniform pressure may result in degraded print quality, wrinkled print media, or other undesirable consequences. As a result, the various fusing assembly components should preferably be mated to close tolerances at room temperature and remain close at operating temperature so that wobble and chattering are minimized.
Electrophotographic image forming devices, such as high speed laser printers, may utilize a fusing system consisting of a fuser roller and associated drive mechanism which may employ a coupled drive hub assembly. The fuser roller typically includes a metal core made of aluminum. The mating fusing assembly includes a hub and collar. The fusing assembly components are commonly fabricated of a steel alloy and may also include drive members such as a steel key. The fusing assembly components may also include an elastomeric collar for minimizing the gap caused by thermal expansion of the fusing system members at operating temperatures, as discussed in U.S. Pat. No. 7,242,899, incorporated herein by reference.
The fuser roller and drive hub assembly rotate at high speed in a single rotational direction. As the imaging device rotates at operating revolutions, instabilities are created by extremely fast stop/start conditions, causing micro machining issues between the contacting surfaces, which eventually develop failure modes of the apparatus. For example, as the imaging device heats from ambient temperature to operating temperatures exceeding 300.degree. F. (148.degree. C.), the components of the fusing assembly expand in relation to their respective coefficients of thermal expansion. The thermal expansion of the aluminum roller core is larger than the thermal expansion of the steel hub components. The thermal expansion of the plastic collar is significantly less than the thermal expansion of both the aluminum roller core and the steel hub components.
The differences in thermal expansion between the various components adversely affects the mechanical stability and operating life of the fuser components. As the imaging device heats to operating temperature, the inside diameter of the fuser roller becomes greater than the outside diameter of the mating components. As a result, a minute level of wobble and chatter can be observed as the fuser roller rotates. The instability of the fuser roller at operating speed and temperature can cause micro machining of the steel hub assembly, plastic collar, and the surfaces of the fuser roller core. Eventually, the instability caused by the gap between the fusing members at operating temperatures may cause catastrophic failure of the fuser roller, plastic collar, or hub assembly. Therefore, a system and method for addressing these and other related problems is desirable.